By-pass vacuum motors are well known in the art. By way of example only, wet vacs are known wherein working air entrained with water is extracted from a surface. Since the working air is entrained with foreign matter such as water and dirt, a separate fan is provided for purposes of generating air flow over the motor for cooling the same. As with all vacuum motors, the operating noise levels associated therewith are becoming of increasing concern. Such noise is generally attributed to the fan tips passing by fixed elements in the fan and motor assembly. Not only is the generated noise objectionable acoustically, it also represents wasted energy. Accordingly, the modern trend is toward the reduction of noise in vacuum motors.
Previously, it has been known to maintain the motor in a housing separate from the fan assembly for drawing the working air. Maintained upon the motor housing is typically a motor cooling fan housing, receiving a fan for drawing cooling air across the motor. A typical prior art motor cooling fan housing is designated generally by the numeral 10 and shown in FIGS. 1 and 2. It will be appreciated that such a fan housing may be molded of plastic or cast of suitable metal. The fan housing 10 typically includes a top plate 12 sealing one end of a cylindrical side portion 14. This cylindrical side portion 14 would typically be open at the other end. In standard fashion, brush clip holders 16 are provided for receiving the motor brushes.
A motor cooling air fan is typically received upon the motor shaft and within the housing 10 immediately beneath the top plate 12. Motor cooling air is drawn by the fan and into the housing 10 through a plurality of segmented ring-shaped openings 18-22. In the embodiment shown, the openings 18-22 are segmented by interposed legs 24-30, generally dividing the ring-shaped openings 18-22 into four slots as shown. The legs 24-30 provide support, strength, and integrity to the top plate 12.
Using the prior art of FIGS. 1 and 2, air is drawn through the slots of the segmented rings 18-22 by a motor cooling fan and over the motor elements. Noise is inherently generated by the air being cut by the edges of the slots. Turbulence or perturbations of air flow result from the fact that the slots of the segmented rings are substantially limited to a circumferential, not radial, directioning of the air. While the fan seeks to draw the air inwardly in a vortex-shape, the slots are not so configured.
It should also be noted from FIG. 2 that the prior art motor cooling fan housing 10 has included a ring 32 extending from an outer peripheral edge thereof and into the cavity of the housing. This ring 32 is provided for purposes of strengthening the assembly and, particularly, the top plate 12. The ring 32 is also provided to shroud the cooling vent fan to prevent recirculation of the cooling air, making the fan system more efficient. The ring depth has typically been on the order of 0.2-0.3 inch, and preferably 0.25 inch. In the prior art, the ring 32 extended only shortly below the top edges of the fan blades, from a minimum of 0.060 inch to a maximum of 0.20 inch. This short extension of the ring has typically allowed a significant noise component of the motor to remain since the tip vortex shedding of air by the cooling air fan remained substantially unrestricted. Further, in the prior art the ring 32 is open at the bottom as shown in FIG. 2, providing an open void between the ring 32 and the cylindrical side portion 14, allowing turbulent air to enter and exit the void, further adding to the noise component.
Accordingly, there is needed in the art a motor cooling fan housing in which air inlets accommodate the air flow from outside the housing into the motor with reduced turbulence, perturbations, air vortex shedding, and resultant noise.